The invention is based on a fuel injection apparatus for a two-stroke internal combustion engine.
A fuel injection apparatus for a two-stroke internal combustion engine is already known (offprint from MTZ, Motortechnische Zeitschrift [Automotive Engineering Journal], 13th year, No. 10, Oct. 1952), in which a fuel injection pump pumps fuel to a fuel injection valve that injects fuel directly into a combustion chamber of the two-stroke engine. The fuel injection pump is embodied as a so-called in-line pump, in which each cylinder of the two-stroke engine is supplied with fuel via a separate pump element. The pump element is composed of a pump piston and a pump cylinder. The pump piston is guided longitudinally displaceably in the pump cylinder and is driven via a drive element by a camshaft of the two-stroke engine. For controlling the performance of the two-stroke engine, a throttle valve rotatably supported in a throttle valve neck is actuated; to that a rod linkage is provided on the throttle valve, the linkage being connected to a gas pedal or a gas lever. In operation of the two-stroke engine, a certain negative pressure is established in the throttle valve neck; this pressure depends on the rotary position of the throttle valve, so that it can be utilized to regulate the supply quantity of the fuel injection pump. In this prior art, the negative pressure is drawn off downstream of the throttle valve and carried via a pulsating pressure line to an adjusting device. The adjusting device is part of the fuel injection pump, and as a function of the negative pressure prevailing in the throttle valve neck it regulates the supply quantity of the fuel injection pump. To vary the supply quantity, the pump piston is rotated, and includes a face which has a recess on its outer jacket in the form of an obliquely extending control edge. By means of the control edge, the pump piston controls a control bore that is in the pump cylinder and discharges into a pump work chamber of the pump piston; the rotary position of the control edge relative to the control bore determines the end of pumping by the pump piston. The useful stroke and thus the supply quantity are varies by means of the location of the pump piston in the pump cylinder.
For rotating the pump piston, a sleevelike control element is provided, the interior of which has an opening with two longitudinal slits; a slaving device embodied on the pump piston, for instance in the form of a piston lug, glides axially displaceably on the longitudinal slits and engages them, so as to rotate the pump piston only when a rotation of the control element occurs. For its actuation, the control element has a toothed segment, which for instance is clamped onto its outer surface and with which a control rod, accommodated crosswise to a longitudinal axis of the pump piston in the housing of the fuel injection pump, meshes with outer teeth, so as to cause a rotation of the control element and pump piston upon a longitudinal displacement of the control rod. In the prior art in question, the control rod is mounted by one end on a diaphragm of an adjusting device, which as a function of the negative pressure in the throttle valve neck determines the supply quantity of the fuel injection pump. To that end, the diaphragm of the adjusting device divides two pressure chambers from one another in pressure-tight fashion, that is, a connection pressure chamber and an adjusting pressure chamber, so that if there is a pressure difference between the connection pressure chamber and the adjusting pressure chamber, the diaphragm is moved in the direction of the pressure drop. As the diaphragm moves, the control rod mounted on the diaphragm is displaced, and at the same time the control element is rotated in order to effect an adjustment of the supply quantity of the fuel injection pump. In this prior art, the adjusting pressure chamber is acted upon by ambient pressure and the connection pressure chamber is acted upon by negative pressure of the throttle valve neck, so that depending on the pressure difference present at the diaphragm, a displacement of the control rod and via the control element a rotation of the pump piston takes place.
In regulating the performance of the two-stroke engine as described by means of a negative pressure in the throttle valve neck, however, it is possible only at extremely inconvenience to adapt the supply quantity to varying operating parameters of the two-stroke engine. Doing so requires additional devices. For instance, the influence of the ambient pressure, which decreases with increasing geodetic altitude and thus a decreasing air fill in the cylinders of the two-stroke engine, can be ascertained only by means of an additional altitude pressure sensor. The influence of the temperature of the air aspirated by the two-stroke engine can also be detected only by means of a temperature sensor that being connected with the fuel injection pumps suitably adapts the supply quantity to the air temperature. Typically, the temperature sensor is accommodated outside the fuel injection pump in the throttle valve neck. The temperature sensor is connected by means of a rod linkage to the fuel injection pump control rod, in order to actuate it in compensating fashion as a function of the temperature of the aspirated air, so that an adaptation of the supply quantity to variable aspirated air temperatures takes place.
Advantages of the Invention
The fuel injection apparatus according to the invention has the advantage over the prior art that in a simple way, an adaptation of the supply quantity of the fuel injection pump to varying operating parameters of the two-stroke engine is accomplished; in particular, the proportions of polluting exhaust gas components and fuel consumption of the two-stroke engine drop markedly.
By means of the provisions recited herein, advantageous further features of and improvements to the fuel injection apparatus disclosed are possible. Advantageously, a starter device that can be turned on upon cold starting of the two-stroke engine makes a further reduction in polluting exhaust gas components possible.